What are the litrage of this box?
"Literage" great word! love it!
12" round tube x 20" long = 1.31 cu ft volume.
That should work OK for typical 8-10" driver designed for sealed box. Too big for 5" full range. But you can add foam blocks to a box that's too big much more easilyer than adding more volume.
To determine the best volume for your specific driver we need to know the driver specs, or just the driver name.
The bigger problem here is that the round baffle shape is literally the worst baffle shape possible for midrange use. It's OK for bass, because bass frequencies are omnidirectional radiation anyway, so the box shape doesn't matter below 500Hz. But for frequencies of a "full range" driver with wavelengths longer than the baffle width, the sound will diffract over the edge, causing fast rolloff of the frequency response. If the baffle edge is equidistant at every radial angle then you will make this dffraction dip as bad as it can possibly be.
Ideally you want the distance from center of driver to the baffle edge to different in every direction, so you minimize the dffraction dip, spread it out over the widest frequency range as possible. For this, a large rectangle baffle shape is good, especially if you mount the driver off center in the baffle. Like a 24 x 36" rectangle baffle, with the center of the 8" driver located so that there is 3" from the right edge of baffle, 6" from the top edge, 9" from the left edge and 12" from the bottom edge. Then the baffle corners add additional variation in distance to the edge. The varying distance make the diffraction happen at different wavelengths (frequencies) so the diffraction dip is flattened across larger bandwidth and less noticeable.
Ironically, a round shape is the ideal baffle shape as long as it is spherical and not flat. Sphere makes the smoothest diffraction rolloff possible while flat round baffle with sharp edge is the worst.
Also, for smaller full range drivers ideally you want the baffle to be as large as possible because this pushes the diffraction frequency lower, so you get more bass, usually this is desired with a full range driver.
https://trueaudio.com/st_diff1.htmhttp://diyaudioprojects.com/Technical/Baffle-Step-Correction-Circuit-Calculator/https://www.t-linespeakers.org/tech/bafflestep/intro-bds.htmlThe last article is written by our own member "planet10"
